This invention relates to the construction and installation of collars by which a flexible duct, such as is used for conducting heated or cooled air, may be joined to a permanently installed rectangular duct, such as is used in the floors of mobile homes and the like.
It is frequently necessary to connect a furnace or air conditioner to such a permanently installed sub-floor duct system by means of relatively large diameter, flexible insulated ducts positioned beneath the mobile home. For this purpose a circular or elliptical opening may be cut in the planar lower surface of the duct and a collar installed therein. On the exterior surface of the collar, the flexible duct is secured by a flexible steel strap or draw band.
Heretofore collars have been used which are completely pre-fabricated, normally at a remote factory. Being generally cylindrical, the space and care required for storage and shipment is undesirably great.
Strapping an insulated duct tightly onto a downward projecting collar imposes substantial hoop compression on it. This adds to the difficulty of designing a knock-down collar which may be field assembled.
For a somewhat analogous use, namely connecting ducts to rectangular registers, knock-down connectors have employed bendable rectangular tabs to be inserted through a rectangular opening in a planar surface of the duct, as in U.S. Pat. No. 3,606,404.